There are some operations where you don't want to do straight set based because it will lock an important table for too long. My usual compromise is a while...

The article said there was a whole lot of configuration management in the front end app. So why not keep it there? Make wrapper sprocs for each set...

where (0=@pUseCondition

or (1=@pUseCondition and d1.[WeekDay]='mon')

or (2=@pUseCondition and d1.[WeekDay]='tue')

Surely it would be more readable to have

where ('none'=@days

or ('mon'=@days and d1.[WeekDay]='mon')

or ('tues'=@days and d1.[WeekDay]='tue')

Why use integers for something like that? ...